1. Field of the Invention
The present invention relates to a backlight unit that emits light, and to a liquid crystal display device that uses the light from the backlight unit.
2. Description of the Related Art
Various kinds of backlight units are conventionally developed that provide light to liquid crystal display panels (non-luminous type display panels) in liquid crystal display devices. As light sources incorporated in area light type backlight units or the like, there may be mentioned, fluorescent tubes, such as hot-cathode tubes or cold-cathode tubes, and LEDs (light emitting diodes).
These light sources, when used in modern slim-type, large-screen liquid crystal televisions (liquid crystal display devices), cause various problems. For example, to emit light to a large-screen liquid crystal display panel, a relatively large number of light sources are required to be incorporated in a backlight unit. This increases the size of the backlight unit itself, and thus makes it difficult to obtain a slim-type liquid crystal television. Furthermore, the use of a large number of light sources leads to an increase in the cost of the backlight unit.
To prevent the size and the cost of the backlight unit from increasing, an increase in the light emission amount of the light sources in the backlight unit is required. With light sources having a large light emission amount (in short, with high-efficiency light sources), the increase in the size of the backlight unit is prevented due to a reduction in the number of light sources, which in turn reduces the cost of the backlight unit.
When the number of light sources in a backlight unit is reduced by employing high-efficiency light sources, however, the intervals between light sources are relatively widened. Consequently, for example, in a case where the light sources are fluorescent tubes, as shown in a sectional view in FIG. 14, the intervals V′ between fluorescent tubes 141 and 141 are widened. As a result, whereas portions over the fluorescent tubes 141 are bright, portions over the intervals V′ between the fluorescent tubes 141 and 141 are dim. (Note that “over” means the direction opposite to the direction from the fluorescent tube 141 to a reflecting frame 142). That is, there arises a relatively large difference in brightness (unevenness in light amount) between the portions over the fluorescent tubes 141 and the portions over the intervals between the fluorescent tubes 141 and 141, and this unevenness in light amount leads to unevenness in the light amount of a liquid crystal display device.
To solve such problems of unevenness in light amount, an idea has been proposed, as in JP 08-122774, of using a multi-layer type light diffusion plate (also called a diffusion unit) including a lenticular lens layer.
The diffusion unit disclosed in JP 08-122774, however, is not used for preventing unevenness in light amount in a liquid crystal display device, but is used for adjusting viewing angle in a liquid crystal display device. Consequently, although the diffusion unit is incorporated in a liquid crystal display device, it is unclear whether or not it can prevent unevenness in light amount.